The object of this grant is to study a number of problems in infants which may be related to 25-hydroxyvitamin D (25-OHD) deficiency: 1) early neonatal hypocalcemia, 2) late neonatal hypocalcemia, 3) rickets and severe osteopenia, 4) Sudden Infant Death Syndrome (S.I.D.S.) and 5) dental hypoplasia. Laboratory determinations and x-rays obtained during the first 3 months of life are to be further correlated with long term growth and development. 73 premature infants, 34 SGA infants, and 8 IDM infants have been enrolled in the study and been prospectively followed. Additional post-mortem samples have been obtained from 23 SIDS and 7 control infants. 8 near-missinfants and 6 infants with late neonatal hypocalcemia seizures have been studied. Analysis of 25-OHD concentrations has been completed in 59 cases and calcium, magnesium, phosphorous and copper have been completed in 100 cases. During the third year, we will concentrate on getting good follow-up of those infants enrolled and obtaining complete dental examinations. We hope to complete analyses of all samples early in the year and begin to correlate laboratory, x-ray and clinical data within the first 3 months. We will also set up a system for analysis of follow-up data related to these earlier findings.